FIELD OF THE INVENTION
The invention relates to a spacer for a fuel assembly of a nuclear power station, in particular for a fuel assembly of a light water reactor.
Spacers are used for fixing fuel rods in a fuel assembly. A spacer forms a matrix of intersecting webs and a base area covered by the spacer corresponds essentially to the cross sectional area of the fuel assembly. Each web has an assembly gap which is disposed at an intersection location with an intersecting web and receives the intersecting web. The webs which are guided in the assembly gaps and subsequently fixed, for example by welding, form cells having an essentially rectangular or square base area. The fuel rods, as well as guide tubes in the case of pressurized water fuel assemblies and possibly water rods in the case of boiling water fuel assemblies, project through the cells formed by the spacer and are held there. In other words, they are fixed in their position relative to the center axis of the fuel assembly.
In certain circumstances, under the operating conditions in the core of the nuclear reactor, the spacers of a fuel assembly may undergo longitudinal expansion which may lead to an increase in the external dimensions of the spacers and consequently of the fuel assembly. In an extreme case, the result of the increase in the external dimensions may be that a fuel rod bundle formed by the spacer can no longer be removed from a fuel assembly box, for example in the case of a fuel assembly for a boiling water reactor.
In the case of fuel assemblies of pressurized water reactors, the longitudinal expansion of the spacers is unusually high. The increase in the external dimensions may cause complications with the adjacent fuel assemblies during servicing work and during loading and unloading of the reactor core.